This invention is directed to devices and equipment for collecting bulk solids, for example, process dust coming from a dust generator, such as a sanding machine, wherein the dust is entrained in a flow of air from the source machine, and is separated out at a dust collection station where the dust falls into a drum, barrel, or similar container. The invention is more specifically directed to a compact and efficient system for collecting and storing production dust from a work area and where the dust is conveyed to a collection station located outside the work area.
For many types of machines for processing a workpiece, some means has to be provided to dispense with the grindings, chips, and particulate matter that is generated by a machine during operation. For example, in the case of wood working machines, such as sanders, joiners, and the like, wood that is removed from a workpiece has to be collected and removed from the work area so as to avoid either a breathing hazard for the workman or a fire hazard. More specifically, in the case of portable equipment, such as floor sanders and edgers, it is conventional to draw off the dust that is generated by the machines and then send the air that is carrying the dust into a filter bag arrangement, or to draw off the dust through a flexible hose or conduit. In such case, the conduit or hose extends from a dust outlet duct of the machine to a collection station. A stream of air is pumped through the conduit, with the entrained process dust. An example of a dust collection system of this general type is shown in U.S. Pat. No. 6,833,016, which is incorporated herein by reference.
Where bulk solids are collected directly inside a drum or barrel, it would be desirable to have the bulk solids collected in a plastic bag or liner for easy removal and disposal.
At the dust collection station, the air flow and entrained process dust are drawn through a cyclone separator disposed atop a storage drum or barrel. The process dust falls into a durable plastic film bag or liner in the barrel, and the air then proceeds to a pumping and filtering arrangement, where the dust-free air is discharged back into the ambient environment. In order to keep the inherent vacuum within the cyclonic separator from drawing the plastic liner out of the barrel, it is typical to have a vacuum hose extending to the wall of the barrel to evacuate the space between the wall of the barrel and the liner. Here the intention is to maintain a vacuum or negative pressure as a bag hold-down feature, to draw and hold the bag against the inside of the barrel. Then, when the bag has been filled to its capacity, the bag can be tied off and lifted out, which eliminates the need to dump the barrel. This also avoids exposure to the operators of the process dust when the collected dust is removed from the barrel for disposal.
In practice, the main dust collection system and the collection container run under a negative air pressure or vacuum relative to ambient. As a result of the negative system pressure, a plastic bag or liner tends to be sucked out of the barrel due to the system vacuum, inducing the liner to collapse, at least partially. This results in the bag not filling completely, or in some cases actually being drawn into the separator, and ripped or torn. Dust collection systems that operate at low pressure need an independent source of higher pressure to hold the liner to the drum.
The previously proposed solution to this has simply been to apply vacuum from the system to the space between the barrel and the liner so as to pull the bag against the walls of the barrel. The intention of this is equalize air pressure outside and inside the plastic barrel liner with the hope that the liner would remain securely in place and achieve the maximum fill volume. However, in operation, the vacuum inside the bag or liner can still exceed that between the liner and the barrel, so it would be preferable to employ a higher vacuum to the bag hold-down arrangement. On the other hand, where a vacuum hose from a vacuum pump is simply inserted into the space between the barrel wall and the liner, there is a tendency for the liner to collapse onto the end of the vacuum hose and block the flow of air into the vacuum hose. This would especially be true if the bag hold-down vacuum is of significantly greater magnitude than the dust collection system vacuum. Also, there is a need to deal with air leaks where the vacuum hose penetrates the wall of the barrel as well as to accommodate air leakage around the rim of the barrel.